Recently, in conjunction with the trend of high packing density and high miniaturization of semiconductor devices, a plasma processing apparatus is employed to perform, such as film forming, etching, and ashing processes in manufacturing semiconductor devices. In particular, given that the apparatus is capable of generating plasma under stable condition even in a high vacuum state at a relatively low pressure in the range of 0.1 to several tens of mTorr, a plasma processing apparatus that processes a wafer by subjecting it to a high-density plasma generated by microwave tends to be used.
Such plasma processing apparatus is disclosed in Japanese Patent Laid-Open Application No. 1-184923, 3-191073, 5-343334 or Japanese Patent Laid-Open Application No. 9-181502 filed by the assignee of the present invention. Here, a typical plasma processing apparatus using microwave is schematically explained with reference to FIG. 11, which illustrates a typical prior art plasma processing apparatus.
As shown in FIG. 11, the plasma processing equipment 2 includes a loading table 6, disposed in a processing container 4 which can be vacuum pumped, for mounting thereon a semiconductor wafer W; in a ceiling portion facing the loading table 6, a microwave transmission window 8 for transmitting microwave, which is made of, e.g., aluminum nitride in disk form, is installed airtight. Specifically, the microwave transmission window 8 is mounted hermetically via a sealing member 14 such as an O-ring or the like on a supporting bracket 12 which protrudes radially inward from a ring-shaped supporting frame member 10 made of, e.g., aluminum, wherein the frame member is installed at an upper portion of the processing container 4.
In addition, disposed on the top surface of the microwave transmission window 8 are, a disc-shaped flat antenna member 16 several mm thick and if necessary, a wave delay member 18 made of, e.g., dielectric material for shortening the wavelength of microwave in the radial direction of the flat antenna member 16. A shield cover body 20 made of a conductor material is provided so as to cover the flat antenna member 16 and the wave delay member 18 while closing the top portion of the processing container 4. Further, installed above the wave delay member 18 is a ceiling cooling jacket 24 with cooling water channels 22 through which cooling water runs to cool the shield cover body 20, and so forth. Moreover, in the antenna member 16, microwave emission holes 26 composed of substantially circular or slit-shaped penetration holes, are formed. In addition, connected to the central portion of the flat antenna member 16 is an internal conductor 30 of a coaxial waveguide 28. A rectangular waveguide 34 is connected to the coaxial waveguide 28 via a mode converter 32 and after that, at the same time, the rectangular waveguide 34 is connected to a matching circuit 36, an isolator 38 and a microwave generating source 40. The matching circuit 36 is adapted to the TE mode among vibration modes of microwave. As a result of this, microwave of, e.g., 2.45 GHZ in the TE mode, which is generated from the microwave generating source 40, is transmitted to the matching circuit 36 and the mode converter 32 through the rectangular waveguide 34. Thereafter, the TE mode of microwave is converted into the TEM mode by the mode converter 32, and the converted microwave is introduced (induced) into the antenna member 16 through the coaxial waveguide 28. Further, microwave in the TEM mode is then propagated in the radial direction of the antenna member 16 and is emitted from the microwave emission holes 26 provided in the antenna member 16 while emitted microwave is transmitted through the microwave transmission window 8. Microwave is then introduced into the processing container 4 disposed in the lower part of the plasma processing equipment; this microwave is used to generate a plasma in the processing container 4, thereby carrying out a plasma process such as etching, film forming, ashing or the like on a semiconductor wafer W.
However, with regard to plasma processing equipment such as above, in the rectangular waveguide 34 or the coaxial waveguide 28, discontinuities are formed at the junctions where they connect with another component member, e.g., the mode converter 32 or the antenna member 16. Consequently, multiple reflections of microwave or the like occur in such discontinuities, inevitably resulting in heat production due to the Joule heat generated from line resistance. In such a case, since the coaxial waveguide 28 or the internal conductor 30 therein is made of a conductor formed of, e.g., brass whose surface is silver-plated, its linear expansion coefficient is relatively large and is about 17.2×10−6/° C. As a result, the coaxial waveguide 28 is deformed by thermal expansion, thereby causing a deformation or a defect in the junctions and, further, a leakage of microwave.
Further, another problem exists as follows. Such a plasma processing apparatus 2 introduces microwave in the TEM mode into the processing container 4. This is because the direction of electromagnetic waves' pointing vector coincides with the direction of current flow. Thus, the antenna can be designed by only considering the phase of the current. However, since a TE-mode matching circuit 36 has been widely utilized in the past, the TE-mode matching circuit 36 has been used in the plasma processing apparatus 2 customarily; and a mode converter 32 for converting the TE mode of microwave into the TEM mode is put in place on the transmission lane of microwave to supply the converted microwave to the flat antenna member 16.
Accordingly, since the mode converter 32 is required, the cost of the plasma processing apparatus increases while the conversion loss of microwave also occurs.
Moreover, since the matching circuit 36 is for the TE mode, it needs to be disposed upstream of the mode converter 32. As a result, the matching circuit 36 must be usually disposed at a site far from the flat antenna member 16 where characteristic impedance would vary substantially, making it impossible to carry out a matching operation of impedance efficiently on occasion.